Human exposure to radiation, whether by accidental or intentional use, has the potential to impact large populations and severely tax the facilities and resources mandated to respond to such incidents. The current state of clinical management of radiation exposure is lacking in its ability to rapidly and reliably provide relevant human dose estimation. Such information is critical for clinicians to make informed decisions regarding the treatment of patients potentially exposed to hazardous levels of radiation. Thus numerous agencies have placed a high priority on the development of novel radiation biodosimetry methods for use in triage situations. This proposal describes the further evaluation of a novel HemAtotoxicity Response Matrix (HARM) that will provide a multiparametric assessment of radiation-induced damage to the hematopoietic system that can be used to estimate dose. The assay is based on the interrogation of whole blood cell populations for alterations in the number of cells present and the health status of these cells. This is accomplished by using a flow cytometer to count cells and measure alterations in mitochondrial membrane potential (MMP) as an indicator of apoptosis. Preliminary experiments demonstrate that the HARM assay is rapid, minimally invasive, inexpensive and has the potential to discriminate clinically relevant radiation doses. The experiments described in this proposal will provide more definitive proof-of-principle data regarding the ability of the assay to meet the requirements of a functional human radiation biodosimeter. Thus, portability studies will determine the ability of the HARM assay to be adopted by other laboratories and the assay's compatibility with mobile flow cytometry instrumentation. The requirement for increased throughput capabilities will be examined via application of automated sample processing technologies and high throughput sample analysis instrumentation to the current method. The intention is to produce a multiparametric assay with high information content that will significantly improve our current ability to determine human exposure to clinically relevant radiation doses. Future studies will investigate the production of highly portable, dedicated instrumentation for field use, a more extensive examination of higher-species responses to irradiation and potential confounding factors such as non-homogenous exposure, combined injury or pre-existing drug effects. By producing methodologies that will improve our ability to characterize the extent and amount of human exposure following a radiological incident, we can more efficiently manage these crisis situations. PUBLIC HEALTH RELEVANCE: In the aftermath of a large-scale human radiation exposure incident, methods that can rapidly estimate an individual's radiation exposure will help clinicians make better decisions regarding allocation of resources to those that require it. This proposal seeks to extend the assessment a novel methodology that can estimate exposure by monitoring the effects of radiation on circulating blood cells. Such technologies will ultimately enhance our nation's ability to manage these hazardous scenarios.